Have you made any purchases within the period up to 1 month before the issue arose?
I’ve struggled with this problem long enough to understand its logic.
If you are one of those lucky people who buy a product, the system marks you and this mark lasts 30 days for it to disappear. This means you can buy a product again 30 days after your last successful purchase. If you are one of those lucky people who are experiencing this problem, I recommend that you buy the products you want in bulk in 30-day periods to minimize the damage this problem will cause to your project because Epic Games officials have no intention of dealing with this problem.